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Accumulation and Coarse Modes Particle Concentrations during Dew Formation and Precipitation

Category: Aerosol and Atmospheric Chemistry

Volume: 18 | Issue: 12 | Pages: 2929-2938
DOI: 10.4209/aaqr.2017.10.0362

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Tareq Hussein 1,2, Larisa Sogacheva3, Tuukka Petäjä2

  • 1 Department of Physics, The University of Jordan, Amman 11942, Jordan
  • 2 Institute for Atmospheric and Earth System Research (INAR / Physics), University of Helsinki, 00014 Helsinki, Finland
  • 3 Climate Change Programme, Finnish Meteorological Institute, 00101 Helsinki, Finland


Dew affects coarse mode particles in a different way than accumulation mode particles.
Dew formation reduces the concentrations of coarse mode particles.
Accumulation mode particle concentration increases with RH.


This study investigates the number concentrations of accumulation mode (0.3–1 µm) and coarse mode (1–10 µm) particles in the eastern Mediterranean urban environment with and without precipitation and dew formation. The results show that the number concentrations of both the accumulation mode and coarse mode particles decreased (with ratios of ~0.7 and ~0.36, respectively) during precipitation. In our analysis, we assumed that dew formation occurred in Amman during nighttime when the relative humidity (RH) was higher than 80% and the difference between the temperature and dew point temperature (i.e., T–DP) was less than 2.5°C. In general, the accumulation mode particle number concentration increased with relative humidity and doubled, on average, during dew formation. On the other hand, the coarse mode particle number concentration was 30% lower during conditions with dew formation than without. The increased number concentration of the accumulation mode particles during dew formation conditions is most likely due to enhanced water vapor condensation on existing ultrafine aerosols (diameter < 0.1 µm), enabling particles to grow to detectable sizes, including the accumulation mode. The decreased number concentration of the coarse mode particles during dew formation conditions may be due to enhanced wet deposition.


Wet deposition Rain Dew Scavenging Semi-arid

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